The hermit thrush, Vermont’s state bird, remains at steady numbers, according to the second Vermont Breeding Bird Atlas set for release this week.

Ask Vermont biologist Rosalind Renfrew how changes in land use and climate may be altering the state and she can stack her desk with scientific studies — or simply speculate on the arrival of the red-bellied woodpecker.

The southern species was once so rare in the Green Mountains it wasn’t recorded by the Vermont Breeding Bird Atlas upon its initial release in 1985. A quarter-century later, the woodpecker is common enough that the second version — edited by Renfrew — reports sightings in seven of the state’s 14 counties.

Vermont boasts more than 200 nesting bird species. The inaugural atlas that chronicled them was the first such state or provincial publication in North America. But the new issue is considered even more newsworthy — Gov. Peter Shumlin unveiled it this past week at a special press conference — because it documents unprecedented shifts.

“This atlas is a portrait of Vermont in flux — great global trends illustrated at a scale of song and feather,” Ripton author and activist Bill McKibben declares on the book’s back cover.

The state from which winter-weary residents traditionally flee now is attracting all sorts of southern flyers, the second edition shows. Conversely, warmer weather is threatening to scare away a few northern natives.

Think all this is for the birds? Vermont birdwatchers annually spend an estimated $50 million. Biologists, for their part, say the state’s ecology is woven together like one big nest. Birds don’t simply sing and fly, they also pollinate plants, disperse seeds and eat insects such as gypsy moths, tent caterpillars and other plant-munching pests that threaten farms and forests.

“We cannot know the nature of Vermont, the health of woodlands, wetlands and other wild places without knowing the status of our birds,” Renfrew says.

Researchers at the private, nonprofit Vermont Center for Ecostudies in Norwich, having posted their findings on the Internet, are ready to release them in book form this week. Everything about the University Press of New England hardcover is big: Six pounds, 576 pages, 208 color photos, 215 graphs, 415 maps, 591 tables. Oh, and the price: $75 — and well worth it, its creators say.

“This book will renew your faith in print,” says Bryan Pfeiffer, an ardent Vermont bird expert who’d gush even if he weren’t a second-edition contributor and publicist. “And this is a case where being second is better than being first — we have a baseline that we can see is changing.”

Launching the state’s most comprehensive bird count a generation ago, 200 volunteers surveyed the state from 1976 to 1981 to collect data for the 1985 atlas. For this year’s follow-up, some 350 returned to the field from 2003 to 2007 in search of similarities and differences.

The new atlas shows some birds are increasing with the help of conservation efforts (the bald eagle, common loon, osprey, peregrine falcon and wild turkey) and maturation of Vermont forests (the barred owl and Cooper’s hawk).

Southern species such as Carolina wrens may be flying north because it’s feeling more like home.

Take the red-bellied woodpecker. Experts speculate its arrival could be sparked by warmer weather. Or more people feeding them. Or more tree cavities for nesting.

“We need to be cautious on attributing changes,” Pfeiffer says. “The atlas only shows trends. Most of the time it doesn’t ascribe cause; sometimes it suggests cause.”

That said, the state has seen a severe decline in most grassland species — the Eastern meadowlark, for one — with the loss of thousands of acres of undisturbed meadowland to haying, forests and development.

“That’s an example how birds are responding to land-use change,” Renfrew says.

Of 19 species that feed on flying insects — “aerial insectivores” such as common nighthawks, flycatchers, nightjars, swifts, swallows and whip-poor-wills — 13 dropped in number. Biologists speculate this may be caused by decreases in prey and in nesting and wintering habitats and increases in mercury and other atmospheric toxins.

Rising temperatures are threatening to reduce the breeding range of several species that prefer cooler climates. Consider the Bicknell’s thrush, a relatively rare songbird that inhabits the spruce and balsam firs that may slowly yield to more southern trees atop such ski summits as Mansfield, Killington and Stratton.

The Bicknell’s thrush is one of 57 birds on the state Fish and Wildlife Department’s “Species of Greatest Conservation Need” list, while the national nonprofit Center for Biological Diversity just sued the U.S. Fish and Wildlife Service to place the bird under the protection of the federal Endangered Species Act.

The news is better for the hermit thrush, Vermont’s state bird: “For a grouping of birds we call interior forest species, by and large they’re doing well and didn’t change,” Renfrew says.

David Sibley, author and illustrator of the Sibley Guide to Birds, calls the atlas “beautiful,” while poet David Budbill deems it “a treasure.” But the photo-rich volume isn’t simply a coffee table book. It’s also full of facts that scientists, students and state planners can tap to maintain and enhance Vermont’s bird population. (The Vermont National Guard already has used it to develop land management guidelines.)

“The Breeding Bird Atlas is based firmly on science,” Shumlin said at his press conference, “but it’s a book for everyone.”

That’s why its creators are donating copies to 150 libraries statewide, as well as posting their findings at www.vtecostudies.org/vbba.

“Birds are indicators of what’s going on in our environment,” Renfrew says. “You have to have a sense of where things stand to know where you want to go. The first atlas set the baseline; the second gives you the bigger picture and a better understanding.”

kevin.oconnor

@rutlandherald.com

For the birds

The new Vermont Breeding Bird Atlas, set for release this week, reports changes in species first counted a quarter-century ago.